Revert 5421 "Fix deadlock on register/unregister observer while ..."

Failure to compile on Chromium Internal bots, because of API changes.

http://chromegw.corp.google.com/i/internal.chromium.webrtc.fyi/builders/Mac/builds/2805/steps/compile/logs/stdio

You need to follow the steps mentioned in 
https://docs.google.com/a/google.com/document/d/1aHrmXECnu3-Jovc2-zYI267EaQCYz-IclYyBp9iA9Fc/edit that of a API changer.

Since I will be rolling the libjingle this week, I can push your changes along with libjingle roll, if you prepare the CLs
as mentioned in the doc.

> Fix deadlock on register/unregister observer while there is a an going callback.
> 
> BUG=2835
> R=mallinath@webrtc.org
> 
> Review URL: https://webrtc-codereview.appspot.com/7119005

TBR=andresp@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/7679004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@5444 4adac7df-926f-26a2-2b94-8c16560cd09d
8 files changed